Cardiac arrhythmias represent a clinically significant disorder of the normal rhythm of the heart and usually require immediate and specific therapy. A common cause of cardiac arrhythmias is coronary artery disease, where a high incidence of arrhythmias has been observed during acute myocardial infarction. Premature ventricular contractions and sinus tachycardia are among the most common types of arrhythmias associated with myocardial infarction. Although these and other types of arrhythmias can be suppressed by the use of antiarrhythmic agents, the prevention of the recurrence of tachyarrhythmias is often necessary for long periods of time or even indefinitely. Consequently, these antiarrhythmic drugs must not only be effective and reliable, but they must have a minimal number of adverse side-effects associated therewith.
The heart is endowed with a specialized excitatory system for generating rhythmical impulses that cause rhythmical contraction of the heart muscle and conductive system for conducting these impulses throughout the heart. A major portion of cardiac disorders is based on abnormalities of this specialized excitatory and conductive system resulting in irregular sinus rhythm. Cardiac arrhythmias as described above, and in particular tachyarrhythmias, are caused by disorders of electrical impulse formation, by disturbances in impulse conduction, or by a combination of the two. Drugs used to treat tachyarrhythmias generally reduce or suppress excitation of the heart muscle by depressing spontaneous diastolic depolarization, and affect conduction by altering the conduction velocity through the myocardial tissue and the duration of the refractory period.
Antiarrhythmic drugs are generally administered on a long-term basis to maintain normal sinus rhythm after electrical cardioversion after normal cardiac action has been restored as alluded to above. Quinidine, 6-methoxy-.alpha.-(5'-vinyl-2-quinuclidinyl)-4-quindinemethanol and disopyramide, .alpha.[2'-(diisopropylamino)-ethyl].alpha.-phenol-2-pyridine-acetamide are two antiarrhythmic agents which depress impulse formation, slow conduction velocity, and increase the duration of the refractory period of cardiac cells; and thus are useful in the treatment of supraventricular and ventricular tachyarrhythmias. However, in addition to the direct effect on the cardiac rhythm, both of these agents exhibit indirect anticholinergic actions which may affect the vagal stimulation of the heart and have an affect on peripheral parasympathetic stimulation.
Both quinidine and disopyramide exhibit adverse side-effects when administered to patients for the management of arrhythmias. The side-effects associated with quinidine include, inter alia, cardiotoxicity, diarrhea, nausea, vomiting, fever, hypertension and depression of myocardial contractility. Likewise, the side effects associated with disopyramide include, inter alia, dryness of the mouth, blurred vision, constipation, and urinary retention, and depression of myocardial contractility.
Changrolin, 4-[3',5'-bis[N-pyrolidinylmethyl]-4'-hydroxyanilino]-quinazoline, an effective antiarrhythmic agent, also possesses substantial anticholinergic activity together with the ability to cause skin discoloration in some patients.
Heretofore, there has not been an effective antiarrhythmic agent available that has not been plagued by one or more of these unwanted, adverse side-effects, many of which are caused by excessive anticholinergic activity. In accordance with the present invention, disclosed are compounds having effective antiarrhythmic activity with less of the unwanted anticholinergic activity associated with these antiarrhythmic drugs.